JP7470566B2 - Fuel cell separator and manufacturing method thereof - Google Patents

Description

The present invention relates to a fuel cell separator and a method for manufacturing the same.

A fuel cell is a battery that extracts energy by utilizing the reaction between hydrogen and oxygen. As the reaction produces only water, fuel cells are known as environmentally friendly batteries. In particular, solid polymer fuel cells are considered promising as batteries for automobiles, communication devices, electronic devices, etc., as they enable high power density and are small and lightweight, and some have been put to practical use. A fuel cell is a cell stack made up of multiple cells stacked on top of each other. Wall members called separators are placed between the cells. The separator is a partition plate that separates the passages for hydrogen and oxygen that are adjacent to each other, and plays the role of allowing hydrogen and oxygen to flow in contact with each other evenly across the entire surface of the ion exchange membrane. For this reason, the separator has grooves that serve as the flow paths.

Separators are broadly classified into metallic and carbon materials based on the material of their construction. Stainless steel, aluminum or its alloy, or titanium or its alloy are generally used for metallic separators. Metallic separators have excellent workability and can be thinned due to the strength and ductility inherent to metals. However, metallic separators have a higher specific gravity than carbon separators described below, which goes against the weight reduction of fuel cells. Furthermore, metallic separators have the disadvantage of low corrosion resistance and forming a passivation film depending on the material. Corrosion of metallic materials or a passivation film is undesirable because it leads to an increase in the electrical resistance of the separator. Coating metallic separators with precious metals by plating or sputtering, etc., increases costs, but a method is known in which the convex parts of the flow paths formed on the surface of the separator are formed with a photoresist film to prevent such high costs (see Patent Document 1).

On the other hand, carbon material-based separators have the advantage of being smaller in specific gravity and more corrosion resistant than metal material-based separators. However, carbon material-based separators are inferior in workability and mechanical strength. There is also a demand for even lower electrical resistance (i.e., even higher conductivity). One method of improving mechanical strength is a separator in which graphite particles are dispersed in a thermoplastic resin (see Patent Document 2).

JP 2011-090937 A JP 2006-294407 A

The method of dispersing graphite particles in a thermoplastic resin can increase the strength of the separator to a certain extent. However, carbon material-based separators are required to be even stronger. They are also required to have high electrical conductivity and excellent gas barrier properties, which are the ability to prevent gas permeation.

The objective of the present invention is to provide a fuel cell separator that has excellent strength, electrical conductivity, and gas barrier properties.

(1) In order to achieve the above object, one embodiment of a fuel cell separator comprises a plate whose constituent materials are granular or fibrous graphite and granular or fibrous resin, and a film, the plate has a groove on a surface thereof as a flow path, and the film includes the groove and the surface of the plate other than the groove, and covers at least the front and back surfaces of the plate.
(2) In a fuel cell separator according to another embodiment, the film may wrap the plate.
(3) In a fuel cell separator according to another embodiment, the film may be a film whose main material is at least one of polyether ether ketone and polyphenylene sulfide.
(4) In a fuel cell separator according to another embodiment, the film may have a thickness of 2 μmm or more and 100 μm or less.
(5) In a fuel cell separator according to another embodiment, the main material of the resin and the main material of the film may be the same type of thermoplastic resin.
(6) In a fuel cell separator according to another embodiment, at least one of the resin and the film constituting the plate may be made primarily of polyphenylene sulfide.
(7) To achieve the above object, one embodiment of a method for manufacturing a fuel cell separator includes a plate containing granular or fibrous graphite and granular or fibrous resin as constituent materials, and a film, and includes the following steps: a first film positioning step of positioning a first film for forming the film within a mold; a molding object positioning step of positioning, on the first film, an object to be molded, which is one of a mixture of at least the graphite and the resin, a grooved plate having grooves on the surface of the plate as flow paths, or a preplate in which the grooved plate does not have grooves; a second film positioning step of positioning a second film for forming the film on the object to be molded; and a molding step of closing the mold with the object to be molded sandwiched between the first film and the second film, and attaching the first film and the second film to the surface of the grooved plate.
(8) In another embodiment of the method for manufacturing a fuel cell separator, the workpiece may be a mixture of at least the graphite and the resin, or the preplate, and the inside of the mold may have an irregularity for transferring the groove, and in the molding process, the mold having the irregularity may be used to mold the mixture or the preplate, form the groove, and adhere the first film and the second film to the front and back surfaces of the molded body of the mixture or the preplate.
(9) In another embodiment of the method for manufacturing a fuel cell separator, the workpiece may be the grooved plate, and the inside of the mold may have projections and recesses that can be inserted into the grooves, and in the molding process, the mold may be used to attach the first film and the second film to the front and back surfaces of the grooved plate.
(10) In another embodiment of the method for manufacturing a fuel cell separator, the molding process may cause the first film and the second film to be bonded together to form a bag-shaped film that encases the grooved plate.
(11) In the method for producing a fuel cell separator according to another embodiment, the resin in the mixture may be a flaky resin powder.
(12) In the method for manufacturing a fuel cell separator according to another embodiment, the main resin material and the main film material may be the same type of thermoplastic resin.
(13) In the method for manufacturing a fuel cell separator according to another embodiment, at least one of the resin and the film constituting the plate may be made mainly of polyphenylene sulfide.

The present invention provides a fuel cell separator with excellent strength, electrical conductivity, and gas barrier properties.

FIG. 1 shows a plan view of a fuel cell separator according to an embodiment of the present invention. FIG. 2 shows a cross-sectional view of the fuel cell separator taken along line AA of FIG. FIG. 3 shows an outline of a manufacturing process for a fuel cell separator according to an embodiment of the present invention. FIG. 4 shows a progress state of the first film arrangement step, the molding target arrangement step, and the second film arrangement step in FIG. 3 in a cross-sectional view of the mold, etc. FIG. 5, which follows FIG. 4, shows a molding step and the progress thereafter in cross-sectional views of the mold and the like. FIG. 6 shows a cross-sectional view of a mold etc. in a molding workpiece placement step when a preplate is used as the molding workpiece in the manufacturing method for a fuel cell separator according to the first modified example. FIG. 7 shows a cross-sectional view of a mold etc. in a molding workpiece placement step in a manufacturing method for a fuel cell separator according to Modification 2, in which a grooved plate is used as the molding workpiece.

Next, an embodiment of the present invention will be described with reference to the drawings. Note that the embodiment described below does not limit the invention according to the claims, and not all of the elements and combinations thereof described in the embodiment are necessarily essential to the solution of the present invention.

1. Fuel Cell Separator Fig. 1 shows a plan view of a fuel cell separator according to an embodiment of the present invention, Fig. 2 shows a cross-sectional view of the fuel cell separator taken along line AA in Fig. 1 and an enlarged view of a portion B thereof.

The fuel cell separator (hereinafter, simply referred to as "separator") 1 according to this embodiment is a plate-like body that is approximately rectangular in plan view. The separator 1 is a plate-like body that is sandwiched from both sides of a membrane electrode assembly (MEA) in a fuel cell, in which both sides of an electrolyte membrane are sandwiched between an air electrode and a hydrogen electrode. In this embodiment, the separator 1 is broadly interpreted to include an anode-side separator arranged on the hydrogen electrode (also referred to as "anode electrode") side, and a cathode-side separator arranged on the air electrode (also referred to as "cathode electrode") side.

The separator 1 has through holes 11, 12, 21, and 22 that penetrate in the thickness direction. The through holes 11 and 21 are arranged on one end side of the separator 1. The through hole 12 is arranged on the other end side of the separator 1 that is opposite to the one end side, facing the through hole 21 when the separator 1 is viewed in a plane. The through hole 22 is arranged on the other end side of the separator 1 that is opposite to the one end side, facing the through hole 11 when the separator 1 is viewed in a plane. A groove 30 is formed as a flow path on one side (front side) of the separator 1. The surface 31 other than the groove 30 is convex with respect to the groove 30. In addition, a groove 32 is formed as a flow path on the surface (back side) opposite the one side of the separator 1. The surface 31 other than the groove 32 is convex with respect to the groove 32.

When separator 1 is a cathode separator, through hole 11 is a supply port for oxidizing gas. Through hole 12 is an exhaust port for oxidizing gas. Through hole 21 is an exhaust port for hydrogen gas. Through hole 22 is a supply port for hydrogen gas. The oxidizing gas is, for example, air, but may be oxygen. Groove 30 on the front side of separator 1 is a flow path for flowing oxidizing gas. Groove 32 on the back side of separator 1 is a flow path for flowing cooling water. In FIG. 1, the flow of oxidizing gas is indicated by white arrows.

When separator 1 is an anode separator, through hole 11 is a hydrogen gas supply port. Through hole 12 is a hydrogen gas exhaust port. Through hole 21 is an oxidizing gas exhaust port. Through hole 22 is an oxidizing gas supply port. Groove 30 on the front side of separator 1 is a flow path for hydrogen gas to flow. Groove 32 on the back side of separator 1 is a flow path for cooling water to flow.

The separator 1 includes a plate 2 and a film 3. The plate 2 is a molded body containing graphite and resin, and has a microstructure in which graphite is dispersed in the resin that has solidified after melting. The graphite constituting the plate 2 is preferably granular or fibrous before molding. The resin constituting the plate 2 is preferably granular or fibrous before molding. Here, granular includes a flake-like (also called thin-piece) form. Furthermore, fibrous includes a whisker-like form. A more suitable combination of the graphite and resin forms before molding is a combination of granular or fibrous graphite and flake-like resin. The plate 2 includes grooves corresponding to the grooves 30 and 32 of the separator 1.

The resin constituting the plate 2 is not particularly limited, but is preferably a thermoplastic resin. A resin more suitable for the plate 2 is a resin with excellent heat resistance, and specific examples thereof include polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyamide (PA), polyether ketone ether ketone ketone (PEKEKK), polyether ketone (PEK), liquid crystal polymer (LCP), polytetrafluoroethylene (PTFE), tetrafluoroethylene-ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), polyimide (PI), polyamide imide (PAI), polyether sulfone (PES), polyphenyl sulfone (PPSU), polyether imide (PEI) and polysulfone (PSU). Among these, PPS or PEEK is particularly suitable. Examples of PPS include M2888 and E2180 manufactured by Toray Industries, Inc., and FZ-2140 and FZ-6600 manufactured by Dainippon Ink and Chemicals, Inc.

The average particle size of the resin used before molding the plate 2 is preferably 1 μm or more and 300 μm or less, more preferably 5 μm or more and 150 μm or less, and even more preferably 10 μm or more and 100 μm or less. Here, the average particle size refers to the particle size measured by a laser diffraction/scattering type particle size distribution measurement method. The measurement method for the average particle size hereinafter is the same.

The graphite constituting the plate 2 may be any of artificial graphite, expanded graphite, natural graphite, etc. Here, expanded graphite refers to graphite or graphite intercalation compounds in which the graphite layers are expanded by intercalating a specific surface of a structure in which regular hexagonal planes of graphite (graphite) are stacked. Examples of expanded graphite include BSP-60A (average particle size 60 μm) and EXP-50SM manufactured by Fuji Graphite Industries Co., Ltd., and examples of artificial graphite include 1707SJ (average particle size 125 μm), AT-No. 5S (average particle size 52 μm), AT-No. 10S (average particle size 26 μm), and AT-No. 10S (average particle size 26 μm), manufactured by Oriental Sangyo Co., Ltd. 20S (average particle size 10 μm), or PAG or HAG manufactured by Nippon Graphite Industries Co., Ltd., and as natural graphite, CNG-75N (average particle size 43 μm) manufactured by Fuji Graphite Industries Co., Ltd., or CPB (scale graphite powder, average particle size 19 μm) manufactured by Nippon Graphite Industries Co., Ltd. can be used. There are no particular restrictions on the shape of the graphite particles, and they can be appropriately selected from flakes, scales, spherical shapes, etc. Furthermore, the graphite may contain a portion of amorphous carbon.

The average particle size of the graphite used before forming the plate 2 is preferably 1 μm or more and 500 μm or less, more preferably 3 μm or more and 300 μm or less, and even more preferably 10 μm or more and 150 μm or less.

Graphite and resin may be mixed together after adjusting the particle size separately and used to form plate 2, or they may be kneaded together first, pulverized, and their particle size adjusted before being used to form plate 2. When graphite and resin are kneaded together, pulverized, and their particle size adjusted, the average particle size of the mixed powder is preferably 1 μm or more and 500 μm or less, more preferably 3 μm or more and 300 μm or less, and even more preferably 10 μm or more and 150 μm or less.

The mass ratio of graphite and resin constituting plate 2 is graphite:resin = 70-95 parts by mass:30-5 parts by mass. For example, 5 parts by mass of resin can be mixed with 70 parts by mass or more and 95 parts by mass or less to form the constituent material of separator 1. Similarly, for example, 30 parts by mass of resin can be mixed with 70 parts by mass or more and 95 parts by mass or less to form the constituent material of separator 1. Separator 1 preferably contains more graphite than resin in mass ratio. A more suitable mass ratio of graphite to resin is 10 parts by mass of graphite, or 10.1 parts by mass or more and 20 parts by mass or less of graphite, per 1 part by mass of resin. As described above, when the parts by mass of graphite are more than the parts by mass of resin, the number of contact points between graphite particles is greater than that of conventional separators, and thus the electrical resistance of separator 1 can be lowered (i.e., the electrical conductivity can be increased). A representative sample of separator 1 has a volume resistivity of 5 mΩcm or less.

The film 3 includes the grooves 30, 32 and the surface 31 of the plate 2 other than the grooves 30, 32, and covers at least the front and back surfaces of the plate 2. That is, the film 3 covers both the front and back surfaces of the plate 2, including the inner surfaces of the grooves 30, 32. The film 3 is made up of two types of film, a first film 4 that covers the front surface and a second film 5 that covers the back surface, which are separated or fused together. In this embodiment, the film 3 is divided into a first film 4 and a second film 5, which are attached to the front and back surfaces of the plate 2, respectively. However, the film 3 may be in the shape of a bag that encases the plate 2 with the first film 4 and the second film 5 joined together.

The film 3 is preferably made of resin or rubber. The film 3 is mainly made of one or more of the above-mentioned preferred options for the resin constituting the plate 2, and more preferably at least one of PEEK and PPS. Here, "main material" means a material that occupies more than 50% by mass of the film 3. The main material may be, for example, 51%, 60%, 70%, 80%, 90%, 95% or 100% by mass, as long as it exceeds 50% by mass relative to the mass of the film 3.

The thickness of the film 3 is preferably 2 μm or more and 50 μm or less, more preferably 4 μm or more and 35 μm or less. If the thickness of the film 3 is 2 μm or more, or even 4 μm or more, the separator 1 can have higher gas barrier performance, higher strength (bending strength), and easier handling. On the other hand, if the thickness of the film 3 is 50 μm or less, or even less than 20 μm, the volume resistance can be lowered. The first film 4 and the second film 5 may have the same thickness or different thicknesses. In this embodiment, strength means bending strength measured according to JIS K7171.

The main material of the resin constituting the plate 2 and the main material of the film 3 can be the same type of thermoplastic resin. In that case, the resin near the surface of the plate 2 and the film 3 covering the plate 2 can be integrated, which further improves the strength of the separator 1. The thermoplastic resin is preferably PEEK or PPS.

2. Method for Producing Fuel Cell Separator Fig. 3 shows an outline of the process for producing a fuel cell separator according to an embodiment of the present invention.

The manufacturing method for a fuel cell separator according to this embodiment is a method for manufacturing a fuel cell separator 1 including a plate 2 containing granular or fibrous graphite and granular or fibrous resin as constituent materials, and a film 3. The manufacturing method includes a first film arrangement step (S100), a molding object arrangement step (S200), a second film arrangement step (S300), and a molding step (S400), and preferably proceeds in the order of S100, S200, S300, and S400.

The first film placement process is a process of placing the first film 4 for forming the film 3 in the mold. The molding target placement process is a process of placing a mixture of at least graphite and resin (one example of a "molding target") on the first film 4. Instead of the mixture, a grooved plate having grooves 30, 32 on the surface of the plate 2, or a preplate in which the grooved plate does not have the grooves 30, 32, may be placed.

The second film placement process is a process of placing the second film 5 for forming the film 3 on the object to be molded. The second film placement process allows the object to be sandwiched between the first film 4 and the second film 5 in the mold. The molding process is a process of closing the mold with the object to be molded sandwiched between the first film 4 and the second film 5, and attaching the first film 4 and the second film 5 to the surface of the plate 2. When the object to be molded is the mixture or the preplate, the molding process allows the formation of the grooves 30, 32, the molding into the shape of the plate 2, and the attachment of the film 3 to the plate 2 to proceed simultaneously. On the other hand, when the object to be molded is a grooved plate, the attachment of the first film 4 and the second film 5 to the plate 2 is performed.

Next, we will explain in more detail the manufacturing method for fuel cell separators.

Figure 4 shows the progress of the first film placement process, the molding object placement process, and the second film placement process in Figure 3 in cross-sectional views of the mold, etc.

(1) First Film Placement Step First, one of the split molds 60 (herein referred to as the "first mold") 40 is prepared (see (a) in the figure). The inside (more specifically, the inner bottom surface) 41 of the first mold 40 has projections and recesses 42 for transferring the grooves 32 formed thereon. Next, the first film 4 is laid on the inside 41 of the first mold 40 so as to cover the projections and recesses 42 of the first mold 40 (see (b) in the figure).

(2) Molding object placement step Next, a mixture 2a, which is at least a mixture of graphite and resin, is placed on the first film 4 placed on the inside 41 of the first die 40 (see (c) in the figure). The mixture 2a is preferably subjected in advance to a process of pulverization and mixing, or a process of only mixing, by a method such as a ball mill. It is preferable that the mixture 2a is placed on the first film 4 with its thickness made more uniform.

(3) Second film placement step Next, the second film 5 is placed over the mixture 2a (see (d) in the figure). As a result, the first film 4, the mixture 2a, and the second film 5 are laminated in this order on the inside 41 of the first mold 40.

Figure 5, following Figure 4, shows the molding process and subsequent progress in cross-section of the mold, etc.

(4) Molding Step Following the second film placement step, the other mold (herein referred to as the "second mold") 50 of the split mold 60 is placed over the first mold 40, and the mold 60 is closed (see (e) and (f) in the figure). The inside (more specifically, the inner bottom surface) 51 of the second mold 50 is formed with unevenness 52 for transferring the groove 30. After closing the mold 60, pressure and heat are applied to mold the mixture 2a (see (g) in the figure). That is, using the mold 60 with the unevenness 42, 52, the mixture 2a is molded, the grooves 30, 32 are formed, and the first film 4 and the second film 5 are attached to the front and back surfaces of the molded body of the mixture 2a. The first film 4 and the second film 5 become the film 3 in a state in which the front surface, the back surface, and part of the side surface (also called the end surface) of the plate 2 are covered. In this embodiment, the film 3 does not completely encase the plate 2, but may be in a bag shape covering the front surface, the back surface, and the end surface of the plate 2. The molding can be performed, for example, in the order of heating at low pressure, heating and increasing the pressure, and cooling under a pressure-holding state. The maximum temperature during molding in the molding process is preferably 300°C or higher and 450°C or lower. For example, when PPS is used for the first film 4 and the second film 5, the maximum temperature during molding is preferably 320°C or higher and 380°C or lower, more preferably 330°C or higher and 360°C or lower. For example, when PEEK is used for the first film 4 and the second film 5, the maximum temperature during molding is preferably 350°C or higher and 450°C or lower, more preferably 360°C or higher and 400°C or lower. The temperature during molding can be appropriately changed depending on the type of the first film 4, the type of the second film 5, and the type of resin used for the plate 2, so that the resin for the plate 2 melts or softens to fix the graphite, and the first film 4 and the second film 5 are closely fixed so as not to be easily separated from the plate 2.

(5) Removal Step After the molding step, the molded body 70 is removed from the mold 60 (see (h) in the figure).

Figure 6 shows a cross-sectional view of the mold and other parts during the workpiece placement process in the manufacturing method for fuel cell separators according to variant 1, when a preplate is used as the workpiece.

In the first modified example, a preplate 80 is used as the molding object, which is a grooved plate without grooves 30 and 32. The preplate 80 is obtained by premolding the mixture 2a in the mold 60 prior to the molding object placement step. Premolding (also called provisional molding or semi-molding) means molding in which the mixture 2a is simply shaped, and the graphite is not completely bonded together with the resin, unlike the case where the plate 2 is completely molded. The fact that the inner side of the mold 60 is provided with projections and recesses 42 and 52 for transferring the grooves 30 and 32 is the same as in the manufacturing method described above with reference to FIG. 4. In the molding object placement step of the first modified example, the preplate 80 is placed on the first film 4 (see (c1) in the figure). In the subsequent molding step, the mold 60 is closed with the preplate 80 sandwiched between the first film 4 and the second film 5 to perform molding, and the first film 4 and the second film 5 can be attached to the surface of the grooved plate.

Figure 7 shows a cross-sectional view of the mold and other parts during the workpiece placement process in the manufacturing method for fuel cell separators according to variant 2, when a grooved plate is used as the workpiece.

In the second modification, a grooved plate 90 is used as the object to be molded. The grooved plate 90 is obtained by pouring the mixture 2a into the mold 60 and molding it prior to the object to be molded placement step. The mold 60 has irregularities 42, 52 on its inside that can be inserted into the grooves 30, 32. In the object to be molded placement step of the second modification, the grooved plate 90 is placed on the first film 4 (see (c2) in the figure). At this time, the irregularities 42, 52 fit into the grooves on the front side and the back side of the grooved plate 90. In the subsequent molding step, the mold 60 is closed with the grooved plate 90 sandwiched between the first film 4 and the second film 5 to perform molding, and the first film 4 and the second film 5 can be attached to the surface of the grooved plate 90.

3. Other Embodiments As described above, the preferred embodiments of the present invention have been described, but the present invention is not limited to these and can be practiced in various modifications.

Groove 30 of separator 1 may be a groove that forms a flow path other than the flow path that flows gas in the direction shown by the white arrow in FIG. 1. Groove 32 may be a groove that forms a flow path of any shape. For example, groove 30 may be a groove that forms a linear flow path from one end of separator 1 to the other end, and groove 32 may be a groove that forms a linear flow path in a direction approximately perpendicular to groove 30. Separator 1 may not have at least one of groove 30 and groove 32.

In the above embodiment, the preplate 80 does not have any grooves equivalent to the grooves 30 and 32, but it may have grooves shallower than the grooves 30 and 32. In that case, when the mold 60 is closed and molding is performed, the preformed shallow grooves can be deepened to change into the grooves 30 and 32.

After the molding process, a trimming process may be performed to trim off excess areas of film 3.

Next, examples of the present invention will be described in comparison with comparative examples. Note that the present invention is not limited to the following examples.

1. Main Raw Materials of Plates (1) Graphite Graphite powder, which is a constituent material of the plates of the fuel cell separator (hereinafter also referred to as "separator"), was 1707SJ manufactured by Oriental Kogyo Co., Ltd.
(2) Resin As the resin for the separator plate, a polyphenylene sulfide (PPS) powder was used. The PPS used was a fine PPS powder obtained by freeze-pulverizing flake-shaped PPS powder of Torelina M2888 manufactured by Toray Industries, Inc. to an average particle size of 50 μm.

2. Pretreatment of raw materials before molding The graphite powder and the resin powder were mixed and pulverized in a ball mill using zirconia balls. The ball mill pulverization was completed when it was confirmed through particle size distribution measurement (measurement by laser diffraction/scattering particle size distribution measurement method) that the particle size of the mixed powder was 90±10 μm on average.

3. Films For the separator films, PPS and polyether ether ketone (PEEK) were used. For the PPS films, several types of films (product numbers: TORELINA 4-1X00, TORELINA 9-3071) manufactured by Toray Industries, Inc. with thicknesses ranging from 4 to 35 μm were used. For the PEEK films, films manufactured by Shin-Etsu Polymer Co., Ltd. with thicknesses of 6 to 35 μm and using raw materials (product number: KT-851NL SP) manufactured by Solvay Specialty Polymers, Inc. were used.

4. Mold The mold used was a top-bottom split mold made of pre-hardened steel NAK80 manufactured by Daido Steel Co., Ltd. When closed, a space (approximately 63 ^cm3 ) was formed inside the mold in which the separator could be molded. In addition, the bottom of the inside of each of the top and bottom dies had projections and recesses for forming the grooves of the separator.

5. Evaluation method (1) Formability of grooves If there were chips or roughness on the appearance of the separator groove unevenness, it was rated as "Failed" (NG). If there were no defects and it was possible to mold it, it was rated as "Passed" (A).
(2) Volume resistivity The volume resistivity of the separator was measured using an apparatus (Loresta-GX T-700) manufactured by Mitsubishi Chemical Analytech Co., Ltd. based on JIS K7194. When the volume resistivity was less than 2.0 mΩcm, it was evaluated as pass (A). When the volume resistivity was more than 2.0 and not more than 3.0 mΩcm, it was evaluated as pass (B). When the volume resistivity was more than 3.0 and not more than 4.0 mΩcm, it was evaluated as pass (C). When the volume resistivity was more than 4.0 and not more than 5.0 mΩcm, it was evaluated as pass (D). When the volume resistivity was more than 5.0 mΩcm, it was evaluated as fail (NG).
(3) Bending Test The bending test of the separator was performed according to JIS K7171 using an apparatus manufactured by Orientec Co., Ltd. (Tensilon Universal Tester RTC-1310A).
Bending strength: When the bending strength was 60 MPa or more, it was evaluated as pass (A). When the bending strength was 50 MPa or more and less than 60 MPa, it was evaluated as pass (B). When the bending strength was less than 50 MPa, it was evaluated as fail (NG).
Bending strain: When the bending strain was 0.80% or more, it was evaluated as pass (A). When the bending strain was 0.65% or more and less than 0.80%, it was evaluated as pass (B). When the bending strain was 0.50% or more and less than 0.65%, it was evaluated as pass (C). When the bending strain was less than 0.50%, it was evaluated as fail (NG).
(4) Gas Permeability Coefficient The gas permeability coefficient of the separator was measured using He gas based on JIS K7126-1 using a gas permeability measuring device (K-315-N-03) manufactured by Rika Seiki Kogyo Co., Ltd. When the permeability coefficient was less than 1.0×10 ⁻¹⁸ mol·m/m ² ·sec·Pa, it was evaluated as pass (A). When the permeability coefficient was 1.0×10 ⁻¹⁸ or more and less than 1.0×10 ⁻¹⁶ mol·m/m ² ·sec·Pa, it was evaluated as pass (B). When the permeability coefficient was 1.0×10 ⁻¹⁶ or more and less than 1.0×10 ⁻¹⁵ mol·m/m ² ·sec·Pa, it was evaluated as pass (C). A permeability coefficient of 1.0×10 ⁻¹⁵ or more and less than 1.0×10 ⁻¹⁴ mol·m/m ² ·sec·Pa was evaluated as pass (D). A permeability coefficient of 6.0×10 ⁻¹⁴ mol·m/m ² ·sec·Pa or more was evaluated as fail (NG).
(5) Overall Evaluation In the evaluation of each characteristic value, the total points of each Example and Comparative Example were calculated as follows: A: 4 points, B: 3 points, C: 2 points, and D: 1 point. The evaluation according to the points is as follows:
AAA grade: Total score 18 points AA grade: Total score 17 points A grade: Total score 16 points or 15 points NG grade: If there is one or more items with an NG grade

6. Manufacturing of Fuel Cell Separators <Example>
(1) Example 1
A 6 μm thick PEEK film was laid on the inner recess of the lower die constituting the split type die, and a powdered mixture (graphite + PPS) after ball mill pulverization was provided on the film. The mixture was a mixed powder of 120 g of graphite powder and 12 g of PPS powder (corresponding to 1000 parts by mass of graphite per 100 parts by mass of PPS). Next, a 6 μm thick PEEK film was placed on top of the mixture so that the thickness of the mixture was almost uniform. Next, the upper die and the lower die constituting the split type die were closed to perform molding. The molding was performed for 3 minutes at a surface pressure of 480 kgf/cm ² so that the temperature of the die rose to 360° C. After molding was completed, the die was opened, the molded body was removed, and the production of the separator was completed. The separator was evaluated by the above evaluation method.
(2) Example 2
A separator was produced and evaluated under the same conditions as in Example 1, except that a 4 μm thick PPS film was used instead of the 6 μm thick PEEK film and the molding temperature was changed from 360° C. to 330° C.
(3) Example 3
A separator was produced and evaluated under the same conditions as in Example 1, except that a 9 μm thick PPS film was used instead of the 6 μm thick PEEK film and the molding temperature was changed from 360° C. to 330° C.
(4) Example 4
Instead of the 6 μm thick PEEK film, a 15 μm thick PEEK film was used.
A separator was produced under the same conditions as in Example 1 and evaluated.
(5) Example 5
Instead of the 6 μm thick PEEK film, a 35 μm thick PEEK film was used.
A separator was produced under the same conditions as in Example 1 and evaluated.
(6) Example 6
A separator was produced and evaluated under the same conditions as in Example 1, except that the holding time of the molding was set to 1 minute.
(7) Example 7
A separator was produced and evaluated under the same conditions as in Example 2, except that the holding time of the molding was 1 minute.
(8) Example 8
A separator was produced and evaluated under the same conditions as in Example 3, except that the holding time of the molding was 1 minute.

Comparative Example
(1) Comparative Example 1
A powder mixture (graphite + PPS) after ball milling was provided in the recess on the inside of the lower die constituting the split die. The mixture was a mixed powder of 99 g of graphite powder and 30 g of PPS powder (corresponding to 330 parts by mass of graphite per 100 parts by mass of PPS). Next, the upper die constituting the split die and the lower die were closed to perform molding. The molding was performed for 3 minutes at a surface pressure of 360 kgf/ ^cm2 so that the mold temperature rose to 320°C. After molding was completed, the die was opened, the molded body was removed, and the production of the separator was completed. The separator was evaluated by the above evaluation method.
(2) Comparative Example 2
A separator was produced and evaluated under the same conditions as in Example 1, except that the mixture (graphite + PPS) was a mixed powder of 120 g of graphite powder and 12 g of PPS powder (corresponding to 100 parts by mass of graphite per 100 parts by mass of PPS).

7. Results Tables 1 and 2 show the production conditions and evaluation results of each of the examples and comparative examples.

For Comparative Example 1, plate formability and volume resistivity were rated NG, bending strength and He gas permeability coefficient were rated B, and bending strain was rated C, resulting in an overall rating of NG. For Comparative Example 2, plate formability, He gas permeability coefficient, and bending strength were rated NG, bending strain was rated C, but volume resistivity was rated A, resulting in an overall rating of NG.

In contrast, for Example 1, plate formability and volume resistivity were rated A, bending strength and bending strain were rated B, and He gas permeability was rated C, resulting in an overall rating of A (total score: 16 points). For Example 2, plate formability and volume resistivity were rated A, bending strength and bending strain were rated B, and He gas permeability was rated D, resulting in an overall rating of A (total score: 15 points). For Example 5, plate formability, bending strength and bending strain were rated A, He gas permeability was rated B, and volume resistivity was rated D, resulting in an overall rating of A (total score: 16 points). For Example 3, plate formability, volume resistivity and bending strain were rated A, bending strength was rated B, and He gas permeability was rated C, resulting in an overall rating of AA (total score: 17 points). For Example 7, the plate formability and volume resistivity were rated A, and the bending strength, bending strain, and He gas permeability coefficient were rated B, resulting in an overall rating of AA (total score: 17 points). Furthermore, for Example 4, the plate formability, volume resistivity, and bending strain were rated A, and the bending strength and He gas permeability coefficient were rated B, resulting in an overall rating of AAA (total score: 18 points). For Examples 6 and 8, the plate formability, volume resistivity, and He gas permeability coefficient were rated A, and the bending strength and bending strain were rated B, resulting in an overall rating of AAA (total score: 18 points).

From the above results, and from a comparison between Comparative Example 1 and Examples 1 to 3, it was confirmed that the effect of using a film on the surface layer was confirmed for any film and thickness. Also, from the results of Examples 1, 4, and 5, it was confirmed that the optimum thickness for the surface layer film was the 15 μm PEEK film of Example 4. Furthermore, from the results of a comparison between Examples 1 and 6, between Examples 2 and 7, and between Examples 3 and 8, it was confirmed that by shortening the molding time to 1 minute, the effect of leaving traces of the resin film on the surface (the presence of a surface layer) was achieved.

The fuel cell separator of the present invention can be used in fuel cells.

1...separator (fuel cell separator), 2...plate, 2a...mixture (an example of an object to be molded), 3...film, 4...first film, 5...second film, 30, 32...groove, 31...surface, 40...first mold (a component of the mold), 41, 51...inside, 42, 52...irregularities, 50...second mold (a component of the mold), 60...mold, 80...preplate (an example of an object to be molded), 90...grooved plate (an example of an object to be molded).

Claims (9)

a plate including granular or fibrous graphite and granular or fibrous resin as constituent materials, and a film consisting only of resin , the plate having a surface on which a groove is provided as a flow path, the film including the groove and the surface of the plate other than the groove, and covering at least the front surface and the back surface of the plate,
A fuel cell separator, characterized in that the thickness of the film is 2 μm or more and 50 μm or less . The fuel cell separator according to claim 1, characterized in that the film wraps around the plate. 3. The fuel cell separator according to claim 1, wherein the film is made of at least one of polyether ether ketone and polyphenylene sulfide. 4. The fuel cell separator according to claim 1, wherein the main resin material constituting the plate and the resin material constituting the film are the same type of thermoplastic resin. 5. The fuel cell separator according to claim 1, wherein at least one of the main material of the resin constituting the plate and the resin constituting the film is polyphenylene sulfide. A method for producing a fuel cell separator according to any one of claims 1 to 5, comprising the steps of:
a first film positioning step of positioning a first film for forming the film in a mold;
a molding object placement step of placing, on the first film, one of a mixture of at least the graphite and the resin, a grooved plate having grooves on a surface of the plate as flow paths, and a preplate in a state where the grooved plate does not have grooves;
A second film placement step of placing a second film for forming the film on the molding object;
a molding process in which the mold is closed while the object to be molded is sandwiched between the first film and the second film, and the first film and the second film are attached to a surface of the grooved plate;
A method for producing a separator for a fuel cell comprising the steps of: the molding object is a mixture of at least the graphite and the resin, or the preplate, and the inner surface of the die is provided with projections and recesses for transferring the grooves;
7. A method for manufacturing a fuel cell separator as described in claim 6, characterized in that in the molding process, the mold having the unevenness is used to mold the mixture or the preplate, form the grooves, and attach the first film and the second film to the front and back surfaces of the molded body of the mixture or the preplate. The molding object is the grooved plate, and the inner side of the die has projections and recesses that can be inserted into the grooves,
7. The method for manufacturing a fuel cell separator as described in claim 6 , characterized in that in the molding process, the first film and the second film are attached to the front and back surfaces of the grooved plate using the mold. 9. The method for producing a fuel cell separator according to claim 6, wherein the resin in the mixture is a flaky resin powder.

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